There exists a need for a reliable synthetic mold release lubricant. The continuous casting of steel is considered as one of the major technological advances in the steel industry in recent years. In conventional steel-making, up to 30% of the steel poured is lost in ingot trimming and mill scale; continuous casting cuts these losses down to 10% or less. Based on the use of 4-6 ounces of lubricant per ton, a substantial market for lubricants for continuous casting of steel is developing.
Without continuous and reliable lubrication of the mold walls, the steel-making process slows down or stops. U.S. Pat. No. 4,152,278 discloses lubricant compositions comprising wax esters of fatty acids and alcohols, particularly advantageous in the continuous casting of steel. These wax esters contain either 0, 1, 2, 3 or 4 internally located carbon-carbon double bonds, with no more than 2 isolated carbon-carbon double bonds being in the fatty acid or the fatty alcohol segments. The fatty acid and fatty alcohol segments are 14 to 17 carbons in length. These wax esters are derived from vegetable oil derivatives and involve the somewhat complicated chemical synthesis comprising reduction of the fatty acid to the fatty alcohol, which is then esterified with the fatty acid with rigorous removal of the water of esterification. Moreover, the compositions prepared are limited by the carbon chain length and the degree of carbon-carbon double bond unsaturation in the original vegetable oil derivative.
Also in the field of lubrication, there exists a need for synthetic, extreme pressure and antiwear lubricant additives. Additives prevent destructive metal-to-metal contact in lubrication at high pressure and/or temperature such as that found in certain gear elements in automotive vehicles and various industrial machines.
Sperm whale oil has been used extensively in these additives. This oil is comprised primarily of wax esters. These wax esters contain either 0, 1 or 2 internally located carbon-carbon double bonds, with no more than 1 carbon-carbon double bond being in the fatty acid or the fatty alcohol segments. The fatty acid and fatty alcohol segments are 15 to 18 carbons in length. Sperm whale oil has good lubricity, good load-bearing ability, and miscibility with the usual types of base oils. However, in 1970, the United States placed the sperm whale on the endangered species list and, in 1971, banned the import of its products.
Jojoba oil has the same properties as sperm whale oil. This oil obtained from the bean of the jojoba plant is pure wax ester. These wax esters contain 2 internally located carbon-carbon double bonds, with 1 carbon-carbon double bond in the fatty acid and the fatty alcohol segments. The fatty acid and fatty alcohol segments are 20-22 carbons in length. In laboratory testing, jojoba oil is comparable or superior to sperm whale oil (Miwa et al., JAOCS 56:765-770 (1979)) as a lubricant additive at high pressure and/or temperature.
However, this natural wax ester source requires 5 years from the date of planting of seedlings before an adequate amount of bean is born for commercialization (National Academy of Sciences, Committee on Jojoba Utilization (1975)). Moreover, the wax esters obtained are limited to 40 to 44 total carbon chain length and di-unsaturation.
The chemical properties which make the above wax esters useful as lubricants are:
1. A carbon chain length for the fatty acid and fatty alcohol segments of at least 14 carbons. PA1 2. The presence of a carbon-carbon double bond in the fatty acid and/or the fatty alcohol segments. PA1 3. The position of the unsaturation being internally, rather than terminally, located.
Microorganisms are a potential source of wax esters. Through metabolic action, wax esters can be produced from inexpensive, readily available hydrocarbons. For example, U.S. Pat. No. 3,409,506 describes the production of wax esters by Micrococcus cerificans (now referred to as Acinetobacter sp. HO1-N) from aliphatic hydrocarbon feedstocks.
Primary advantages of microbial production of wax esters are in the ability and flexibility in controlling the carbon chain length of the fatty acid and the fatty alcohol segments and the degree of unsaturation present. Thus, for example, if a C.sub.16 hydrocarbon is employed as the feed, the principal wax ester will have a carbon chain length of 16 for the fatty acid and fatty alcohol segments. The primary disadvantage of previous reports on microbial production of wax esters is that saturated, not unsaturated, wax esters are formed. The presence of the carbon-carbon double bond in the fatty acid and/or the fatty alcohol segments in necessary to impart the desired lubrication properties. U.S. Pat. No. 3,409,506 discloses that Micrococcus cerificans produces only cetyl palmitate (saturated wax ester) from hexadecane. Stewart et al., J. Bact. 78:726-730 (1959) state that Micrococcus cerificans produces only octadecyl stearate (saturated wax ester) from octadecane. Makula et al., J. Bact. 121:250-258 (1975) claim that only 1 wax ester component (cetyl palmitate, saturated wax ester) is formed by Acinetobacter sp. HO1-N acting on hexadecane. Raymond et al., Adv. Appl. Microbiol. 14:93-121 (1971) and Krasilnikov et al., Mikrobiologiya 38:757-760 (1969) state the same finding (hexadecane yields cetyl palmitate only) for Nocardia species and Mycobacterium species, respectively. It has never been reported that microorganisms can produce wax esters containing carbon-carbon double bonds by metabolic action on saturated hydrocarbons. Saturated hydrocarbon feedstocks are expected to yield saturated wax esters according to present state of the art.
Attempts have been made to produce wax esters containing carbon-carbon double bonds by feedstocks other than saturated hydrocarbons. The metabolic action of Acinetobacter sp. HO1-N (Makula et al., J. Bact. 121:250-258 (1975)) and 3 species of Acinetobacter (Gallagher, J. Gen. Microbiol. 68:245-247 (1971)) on amino acid feed stocks yielded unsaturated wax esters. Fixter et al., Biochem. Soc., Transl. 4:504-505 (1976), reported that the metabolic action of Acinetobacter species on acetate or succinate feedstocks yielded wax esters containing C.sub.14, C.sub.16 and C.sub.18 saturated and mono-unsaturated fatty acid and fatty alcohol segments. The high cost of these substrates relative to aliphatic hydrocarbon feeds is a disadvantage. The metabolic action of Candida lipolytica on olefinic feedstocks yielded unsaturated wax esters (Stewart et al., Science 132:1254 (1960)). The high cost of unsaturated hydrocarbon feeds relative to saturated ones is a disadvantage. Moreover, the carbon-carbon double bond is in the terminal position on the wax esters. The unsaturation needs to be internal, rather than terminal, to impart the much needed oxidative stability.